1. Field of the Invention
The present invention relates to imaging systems, and, more particularly, to a method for calculating a print medium pick time for an imaging apparatus, such as an electrophotographic machine, that transports print media at variable speeds.
2. Description of the Related Art
In known electrophotographic machines, a sheet of paper is picked from an input device, such as a paper tray, prior to the start of the imaging process on a developing unit. As the paper moves through the paper path at a constant speed, the leading edge of the paper eventually actuates a paper path sensor which signals the machine to commence imaging onto the developing unit. The image is laid down on a single rotating photoconductive drum in the developing unit. Eventually, the image on the drum is transferred to a transfer medium and then onto a sheet of paper which contacts the transfer medium at a precise point in time in order to establish a desired top writing line margin. This process is repeated for each individual sheet of paper, allowing the machine the luxury of waiting until each page is at a known location in the paper path before beginning the imaging process. Since the paper is picked prior to imaging, thereby allowing the electrophotographic process to wait for the paper to arrive at a certain location before commencing imaging, the margin above the top writing line on the paper can be accurately controlled.
It may be desirable or necessary to design an electrophotographic machine such that imaging is begun on a developing unit before the sheet of paper is even picked from the input device. This requirement may be due to size limitations on the printer which reduce the maximum length of the paper path. It may also be due to the use of multiple developing units, each transferring an image of a respective color onto a same location on the transfer medium. That is, after an image is first scanned onto a photoconductive drum for a first color, the image is transferred onto an intermediate transfer medium belt. The belt then moves over to receive an image of a second color from a second photoconductive drum. The second image is received on top of and overlaps the first image. This process repeats for each of the photoconductive drums, and the completed composite image eventually reaches the paper transfer nip where it is transferred from the intermediate transfer medium belt onto the paper. Since additional time is required for transferring a separate image from each developing unit sequentially, it may be necessary to begin imaging on at least a first of the developing units before the paper is picked from the input device.
A variable sheet transfer velocity profile is used in order to allow a sheet of print medium picked from a given media source tray to arrive at the image transfer location at the proper time and at the proper velocity to accommodate an accurate location of the top margin of the image to the sheet. Such a use of a variable sheet transfer velocity profile, however, complicates the task of picking a sheet of print medium from a given tray at an appropriate time.
What is needed in the art is a method for calculating a print medium pick time for an imaging apparatus, such as an electrophotographic machine, that transports print media at variable speeds.
The present invention provides a method for calculating a print medium pick time for an imaging apparatus, such as an electrophotographic machine, that transports print media at variable speeds.
The invention comprises, in one form thereof, a method for calculating a print medium pick time for an imaging apparatus that transports media at variable speeds along a media path. The method includes the steps of providing a media path sensor for sensing an arrival of a media sheet at a known location along the media path; providing an image on an image transfer member; providing an image transfer location adjacent the media path; providing a staging process for varying a transport velocity of the media sheet before transferring the image to the media sheet at the image transfer location, the staging process being used for positioning a top writing line margin of the media sheet in relation to the image at the image transfer location; determining a time period t1 corresponding to a time when a pick motor is started to pick the media sheet to a time when the staging process is started; determining a derived time period t2 representative of a normalized time from when the staging process is started to a time when the media path sensor senses the media sheet; and determining a compensated calculated pick time for the media sheet by summing the time period t1 with the time period t2.
In another form thereof, the invention comprises a printer. The printer includes a media tray for holding media sheets. A pick motor is provided for picking a media sheet from the media tray. A staging system is provided and includes a staging motor operating in accordance with a staging process effecting a staging algorithm for transporting the media sheet along a media path. A staging motor encoder is coupled to the staging system for determining a distance traveled by the media sheet. A sensor is provided for sensing an arrival of the media sheet at a known location along the media path. A microcontroller is provided for executing computer instructions to determine a compensated calculated pick time (CPTcomx) for the media sheet, the computer instructions effecting the equation:
CPTcomx=Staging_Encoders_From_Staging_Algorithm_Start_To_S2_Make/Staging_Encoders_Per_Second_At_Normal_Process Speed+Staging_Start_TimeStamp_Pick_Start_TimeStamp
wherein:
Staging_Encoders_From_Staging_Algorithm_Start_To_S2_Make is a number of staging motor encoder pulses counted from when the staging algorithm starts until the sensor detects the media sheet;
Staging_Encoders_Per_Second_At_Normal_Process_Speed is set to a number of encoder pulses per second that should occur if the staging motor was rotating at a known process speed;
Staging13 Start13 TimeStamp is a system time of the printer when the staging algorithm is started; and
Pick_Start_TimeStamp is a system time of the printer when the pick motor is started.
An advantage of the present invention is that an accurate pick time can be established for a media sheet in an imaging system that transports print media sheets at variable speeds.
Another advantage of the present invention is that it minimizes the need to make extreme staging changes in positioning a media sheet in relation to an image.
Still another advantage is that the present invention can be implemented using existing hardware within the imaging apparatus.